Hydrometallurgy refers to the dissolution of ores using aqueous solutions. Generally, three steps make up the process. These are:
1. The use of an aqueous solution to leach the metal.
2. Removal of impurities from the solution.
3. Recovery of the metal (or its compound) from the solution.
The aqueous solution used for leaching is often an acid solution. These acids can include, but are not limited to, sulfuric acid, nitric acid, hydrochloric acid, acetic acid and phosphoric acid. Such acids and metals in general are certain targets for recovery by the present invention.
As an example of acid use, dilute sulfuric acid is used to leach oxide ores such as zinc oxide. Another example is using recycled sulfuric acid for leaching waste rock and overburden at copper mines.
We have discovered that the use of the present invention provides an efficient method for recovering acid used in hydrometallurgical applications. Industrial benefits include allowing for the recycling of the acid solution where recycling is not normally used, improved efficiency and cost effectiveness of acid recovery, where recovery is already used, and improved efficiency/recovery of metals.
Presently, it is known to those ordinarily skilled in the art to purify and recover acid using acid retardation utilizing batch (fixed bed) chromatography columns or with Higgins loop systems. Acid retardation is a method for selectively extracting strongly dissociated acids from solutions typically using strong-base type anion exchange resins. A feed solution is passed over a strong-base type anion exchange resin. The resin, for instance, has a greater affinity for the acid than for salts, resulting in separation of salts from the acid which has its movement retarded by the resin's affinity. The acid typically is displaced from the resin by a pulse of fresh water.
Acid retardation carried out in fixed bed or column chromatography systems utilize a batch mode with feeding of solution followed by elution with water. The foregoing method is the simplest to configure and understand but is typically the least efficient with respect to resin loading and eluent use. The Eco-Tech Acid Processing Unit (APU) is an example of this type of system.
The Higgins loop is equipment that requires a complicated intermittent pulsing of resin around a closed loop made up of reacting sections. The resin moves in one direction while the liquid moves in the other. Although Higgins loops can be more efficient than batch chromatographic systems, they exhibit a number of problems. In particular, the movement of the resin typically results in resin degradation over time. It is generally noted that many of today's mining methods were introduced as early as the mid-19th century.